Cytoskeleton

Question 1

cytoskeleton

Answer 1

• Fibrous proteins found in cytoplasm, not in the nucleus
• 3 parts
  1. Intermediate filament (10 nm)
  2. Microtubules (25 nm) (b/c there is a hole in the center)
  3. Actin filaments (7 nm)

Question 2

Immunofluorescence

Answer 2

• technique for visualizing the cytoskeletal elements

- antibody to a specific protein target

Question 3

antibody

Answer 3

• protein (dimer) shape of a Y, at the two top branches–> areas called antibody (Ab)
• specific binding site for antigen (target)
• part of immune system
• ex. isolate intermediate filaments- isolate major component and inject into mouse, inject into rabbit–> rabbit will have immune response to the protein; recognize it as a foreign protein
  –> rabbit will start making these kinds of antibodies (millions) so in the future, they will stick to it and kill it off

Question 4

Intermediate filaments

Answer 4

• shape & strength of cell- anchor and keep cell in place
• intermediate filaments assemble on top of each other, twisted together
• also part of the junction in epithelial cell
• ex. keratin in skin, neurofilaments in neurons, Nuclear lamin in nuclear envelope

Question 5

Microtubules

Answer 5

• tube w/ lumen, 13 rows of filament
• made up of tubulin dimers (protein)- 3-D shape, tertiary structure
• quaternary- alpha and beta tubulin assemble to create dimers=microtubule subunit
• Dimers are assembled at one end and form tube spontaneously
• line of tubulins= protofilament (don’t assemble in line)- always 13
• (+ and - end)- alpha (-) end assembles slower than beta (+) end

Question 6

Microtubule locations

Answer 6

1. interphase cell- when not dividing- scattered throughout the cytoplasm they emanate out from centrosome
   - -> MTOC (microtubule organizing center/call center)
2. dividing cell- mitosis- Two cell centers and microtubules are emanating out and hold onto chromosomes to pull to opposite poles
3. Ciliated Cell- cilium help things beat to move past the cell/swim
4. Flagellated Cell- only sperm cell

Question 7

Centrosome

Answer 7

area near nucleus with emanating microtubules
centrosome always has a pair of centrioles (short/barrel like, right angles) at the cell center
–>9 groups of the 3 microtubules
–> arrangement is referred to as 9 + 3
–> in centriole and basal body, it is 9+0

Question 8

Cilia and flagella

Answer 8

• work in the same way have beating motion
  only in Eukaryotes–> different from in prokaryotes/bacteria where motion is rotary
• both 9+2 arrangement

Question 9

tubulin

Answer 9

protein made up of 100+ amino acids

2 types- alpha and beta

Question 10

centriole

Answer 10

• always occur in pair- 2 centrioles at the cell center
• made of 3 microtubules fused together and then there are groups of those fused microtubules
• Always 9 groups of 3 microtubules
  open space in the middle–> 9+0
• do not have dynamic instability

Question 11

dynamic instability

Answer 11

• at ay particular moment for any particular microtubule, it may be elongating or shrinking
  to establish the cell shape that it wants and to move things around in the cell
• Ends- plus (grows longer faster), minus (grows slowly)

Question 12

GTP

Answer 12

energy molecule- gunaosine triphosphate

• microtubule dimer binds with GTP molecule, GTP increases tendency to assemble dimers
• As the GTP sits around, it hydrolyses so the GTP gets broken by the tubulin molecule and becomes GDP + a free phosphate (Pi)
• once Pi is released, GDP has a tendency to disassemble

Question 13

inorganic phosphate

Answer 13

free phosphate (Pi)
from hydrolysis of GTP--> GDP + Pi

Question 14

GDP Gap

Answer 14

when GTP bound to tubulin dimers, assembly is faster than hydrolysis –> have a GDP cap
If the process slows and goes in reverse (bc of dynamic
instability), we have paused, and a short amount of time has passed and GTP’s hydrolyze and then GDPs form and everything shrinks.
Pi comes off of GTP and it floats away in aqueous medium –> left with GDP

Question 15

cilia and flagella

Answer 15

cilia- short and beat (don’t rotate), many (50+), on lung cells (beat out mucus to trachea–> clear throat), all over paramecium, lung infection can kill epithelial cells–> cough after because forming new epithelial cells

flagella- only on sperm in humans, organisms only have 1-3, long and thin

Question 16

microtubule motors

Answer 16

• mechanism behind bending/beating
• each pair of MTs have one pair of motors that reach out and grab onto the next pair and try to walk along it
• when ATP present, causes motor to walk along and push other side down so it moves up (motors walk towards (-) end)
• microtubules are held together –> causes bending instead of sliding

Question 17

Axoneme

Answer 17

• complex internal structural components of a flagellum or

cilium (not including the membrane)

Question 18

basal body

Answer 18

• at the bottom of every flagellum or centriole

- centriole that is now being used as an anchor for the base of a flagellum or cillium

Question 19

internal spokes

Answer 19

• connecting proteins inside the MT

- causes bending when MT begins to walk along another

Question 20

bending action

Answer 20

With ATP:
dynein motor causes MT to slide in isolated doublet
dynein motor causes MT to bend when proteins are linked (flagella)
dunein have motor like feet

Question 21

Neuron MT

Answer 21

-when NTs are ready to be delivered to axon
–> NT packed in cell body in a vesicle, placed on track, motor walks them down and sticks onto microtubule and moves down
– Membranes are recycled from axon and brought back to cell body
BIdirectional transport
–> Dynein motor carries things back to cell body (from + to -)
–> Kinesin motor carries things (vesicles) towards the axon (from – to +)

Question 22

motor protein (dynein and kinesin)

Answer 22

• MT motor attaches to ATP
• hydrolysis ATP to ADP and phosphate
• back end moves, puts its foot down again, and then releases ADP–> causes front foot to pick up and now it’s back at starting condition
• As long as there are ATPs, there are feet to keep moving, which causes motor to walk along the microtubule
  next

Question 23

actin filament function (globular actin/g actin)

Answer 23

make actin, assembles into a higher order fiber

1. an epithelial cell with a bunch of folds that increase areas of absorption in the gut (microvilli supported by actin)
2. anchor cell into substrate and it runs actin filaments in between adhesion spots
3. crawls along substrate- actin filaments depolymerize into g-actin–> increases the # of particles, water of the cell moves toward the bottom of the cell, cell will move in that direction because of osmosis
4. dividing cell, we have microtubules separating chromosomes–> actin wraps around cell and pinches it

Question 24

Filamentous actin

Answer 24

Take individual globular actins and bind it to itself to make a long strand and TWO strands wind up together

Question 25

Microvilli

Answer 25

All of things on the side supporting fingers are actin | filaments

Question 26

actin treadmilling

Answer 26

- different than dynamic instability - can assemble or disassemble at either end - adding on one end, falling off the other end at the same rate, length doesn’t change - ATP assembles, ADP disassembles

Question 27

capping actin filaments

Answer 27

- some drugs, like cytochalasin, cap the actin filaments and prevent them from elongating - can prevent the growth of cancerous cells

Question 28

extracellular matrix (ECM)

Answer 28

ECM secreted by the cell • help cells anchor in place • Connect with other cells • Create an environment that the cells like to live in • Long firs, like proteoglycan and collagen (protein structures secreted outside the cell) • transmembrane proteins- anchor outside fiber network to inside fiber network

Question 29

desmosome

Answer 29

- holds cells together | - intermediate filament attaches to desmosome

Question 30

chemotherapy drugs

Answer 30

- target cell division - can upset stomach and hair growth because lots of cell division there - preventing tubulin polymerization

Question 31

fibrous structures

Answer 31

- elastin- allows skin to stretch - collagen- resists stretch - extracellular matrix- where fibers are found - integrin- holds together fibers